As a sliding member such as a plain bearing used in a crankshaft or a connecting rod of an automotive engine, a bearing is often used which includes a bearing alloy of a Cu (copper) alloy or an Al (aluminum) alloy lined on the surface of a back steel. The bearing has a coating layer deposited on the surface of the bearing alloy (base material) through an intermediate layer by electroplating. The coating layer is provided for the purpose of further improving bearing characteristics such as conformability with an opposite material, and the intermediate layer is provided for improving a bonding strength between the bearing alloy and the coating layer.
Conventionally, an alloy containing Pb (lead) and Sn (tin) as main components has been used as a metal composing the coating layer. Among them, Pb (lead) is an environmental contamination substance, so that a Pb-free material has been pursued. It is proposed to use Bi as its substitute material, which has a low-melting point similar to Pb. However, Bi in its natural state cannot be used as a material for forming a coating layer to which fatigue resistance and conformability are required, because it is hard and fragile. In order to improve the properties of hardness and fragility of Bi, various kinds of improvements have been made (for instance, see JP-A-11-50296, JP-A-2003-156045, or JP-A-2004-308883.